Dose-guided radiation therapy using cone beam CT

Abstract

A system includes acquisition of a three-dimensional cone beam image, and determination of a dose to be delivered based on the three-dimensional image and on parameters of a treatment beam to deliver the dose. Some systems may include modification of a three-dimensional cone beam image to correct for scatter radiation, and determination of a dose based on the modified three-dimensional cone beam image.

1. A method comprising:
 acquiring a three-dimensional cone beam image; and 
 determining a dose to be delivered based on the three-dimensional image and on parameters of a treatment beam to deliver the dose, 
 wherein determining the dose comprises: 
 determining an electron density value associated with each of a plurality of voxels of a modified three-dimensional cone beam image; 
 delivering treatment radiation according to a treatment plan; 
 acquiring a portal image during delivery of the radiation; 
 determining a map of treatment beam energy fluence based on the portal image; 
 determining an entry dose based on the map of treatment beam energy fluence and the electron density value associated with each of the plurality of voxels; and 
 determining the dose delivered to each of the plurality of voxels based on the entry dose and the electron density value associated with each of the plurality of voxels. 
 
   
   
     2. A method according to  claim 1 , further comprising:
 changing the parameters of the treatment beam to second parameters based on the determined dose. 
 
   
   
     3. A method according to  claim 2 , wherein changing the parameters of the treatment beam based on the determined dose comprises:
 spatially registering the determined dose with a planned dose; 
 determining a difference between the spatially-registered determined dose and the planned dose; and 
 determining the second parameters based on the determined difference. 
 
   
   
     4. A method according to  claim 1 , wherein acquiring the three-dimensional cone beam image comprises:
 acquiring a plurality of two-dimensional images using megavoltage radiation; and 
 generating a three-dimensional image based on the plurality of two-dimensional images. 
 
   
   
     5. A method comprising:
 modifying a three-dimensional cone beam image to correct for scatter radiation; and 
 determining a dose based on the modified three-dimensional cone beam image, 
 wherein modifying the three-dimensional cone beam image comprises: 
 registering the three-dimensional cone beam image with a previously-acquired three-dimensional image; 
 determining a plurality of voxel ratios based on image values of each of a plurality of voxels of the previously-acquired three-dimensional image and image values of each of a plurality of associated voxels of the registered three-dimensional image; and 
 determining a volume ratio associated with each of a plurality of volumes of the registered three-dimensional image, each of the volume ratios based on a plurality of the determined voxel ratios; and 
 modifying each of the plurality of volumes of the registered three-dimensional image by an associated volume ratio. 
 
   
   
     6. A method according to  claim 5 , further comprising:
 changing a next treatment fraction based on the determined dose. 
 
   
   
     7. A method according to  claim 6 , wherein changing the next treatment fraction based on the determined dose comprises:
 determining a difference between the determined dose and a planned dose; and 
 changing the next treatment fraction based on the difference. 
 
   
   
     8. A method according to  claim 5 , wherein modifying the three-dimensional cone beam image to correct for scatter radiation comprises:
 acquiring a plurality of two-dimensional images using megavoltage radiation; 
 modifying each of the plurality of two-dimensional images to correct for scatter radiation; and 
 generating the three-dimensional cone beam image based on the modified two-dimensional images. 
 
   
   
     9. A method according to  claim 5 , wherein modifying the three-dimensional cone beam image comprises:
 determining a geometric model of correction factors to characterize a cupping artifact of scatter radiation; and 
 modifying the three-dimensional cone beam image based on the geometric model. 
 
   
   
     10. A method according to  claim 5 , wherein the previously-acquired three-dimensional image is acquired by a computed tomography scanner. 
   
   
     11. An apparatus comprising:
 a linear accelerator to generate a treatment radiation beam associated with a plurality of treatment beam parameters; 
 a portal imaging device to acquire a plurality of two-dimensional images based on the treatment radiation beam; and 
 a processor to generate a three-dimensional image based on the plurality of two-dimensional images, and to determine a dose to be delivered by the treatment radiation beam based on the three-dimensional image and on the plurality of treatment beam parameters, 
 wherein determination of the dose comprises: 
 determination of an electron density value associated with each of a plurality of voxels of a modified three-dimensional cone beam image; 
 delivery of treatment radiation according to a treatment plan; 
 acquisition of a portal image during delivery of the radiation; 
 determination of a map of treatment beam energy fluence based on the portal image; 
 determination of an entry dose based on the map of treatment beam energy fluence and the electron density value associated with each of the plurality of voxels; and 
 determination of the dose delivered to each of the plurality of voxels based on the entry dose and the electron density value associated with each of the plurality of voxels. 
 
   
   
     12. An apparatus according to  claim 11 , wherein the processor is to change at least one of the plurality of treatment beam parameters based on the determined dose. 
   
   
     13. An apparatus according to  claim 12 , wherein the processor is to change at least one of the plurality of treatment beam parameters by:
 spatially registering the determined dose with a planned dose; 
 determining a difference between the spatially-registered determined dose and the planned dose; and 
 determining at least one new treatment beam parameter based on the determined difference. 
 
   
   
     14. An apparatus comprising:
 a linear accelerator to generate a treatment radiation beam; 
 a portal imaging device to acquire a plurality of two-dimensional images based on the treatment radiation beam; and 
 a processor to modify a three-dimensional cone beam image to correct for scatter radiation and to determine a dose based on the modified three-dimensional cone beam image, 
 wherein modification of the three-dimensional cone beam image comprises: 
 registration of the three-dimensional cone beam image with a previously-acquired three-dimensional image; 
 determination of a plurality of voxel ratios based on image values of each of a plurality of voxels of the previously-acquired three-dimensional image and image values of each of a plurality of associated voxels of the registered three-dimensional image; and 
 determination of a volume ratio associated with each of a plurality of volumes of the registered three-dimensional image, each of the volume ratios based on a plurality of the determined voxel ratios; and 
 modification of each of the plurality of volumes of the registered three-dimensional image by an associated volume ratio. 
 
   
   
     15. An apparatus according to  claim 14 , the processor further to change a next treatment fraction based on the determined dose. 
   
   
     16. An apparatus according to  claim 15 , wherein changing the next treatment fraction based on the determined dose comprises:
 determining a difference between the determined dose and a planned dose; and 
 changing the next treatment fraction based on the difference. 
 
   
   
     17. An apparatus according to  claim 14 , wherein modifying the three-dimensional cone beam image to correct for scatter radiation comprises:
 acquiring a plurality of two-dimensional images using megavoltage radiation; 
 modifying each of the plurality of two-dimensional images to correct for scatter radiation; and 
 generating the three-dimensional cone beam image based on the modified two-dimensional images. 
 
   
   
     18. An apparatus according to  claim 14 , wherein modifying the three-dimensional cone beam image comprises:
 determining a geometric model of correction factors to characterize a cupping artifact of scatter radiation; and 
 modifying the three-dimensional cone beam image based on the geometric model. 
 
   
   
     19. An apparatus according to  claim 14 , wherein the previously-acquired three-dimensional image is acquired by a computed tomography scanner.